Cyclophosphamide (CP), an antineoplastic and immunosuppresive agent, even when administered in large doses, slightly affects the quantity of blood platelets. The aim of the present study was to analyse the effect of single intraperitoneal administration of CP (150mg/kg b.w.) on the quantitative changes in platelets obtained from the left and right ventricle of the heart, as well as to evaluate the occurrence of megakaryocytes in lung tissue depending on the period of time that passed from CP administration.In control subgroups, fewer platelets were found in the blood collected from the RV compared with the left ventricle at all time intervals. After 1 and 3 days following i.p, administration of CP, a decrease was observed in the number of platelets both in the blood from the right ventricle and left ventricle when compared with control. However, after 14 days, the number of platelets in the blood from the left ventricle was higher, compared with the left ventricle and right ventricle of control animals, and significantly higher (p<0.001747), compared with their number obtained from the right ventricle of CP-receiving animals.Simultaneous ultrastructural examinations with transmission electron microscopy revealed the increased number of platelets in the lung vascular bed of CPreceiving rats at all time intervals. However, megakaryocytes were found 7 and 14 days after administration of CP. The findings clearly indicate that the lungs could be a major place of thrombopoiesis following therapy with a single large dose of CP
